Broadband cup dipole antennas are generally well known for generating uniform radiation patterns in the electric (E) and magnetic (H) planes.
One problem with prior art broadband cup antennas, which use large elements for the monopoles, is that the relatively large size of the monopoles brings the edges of the monopoles close to the cup walls, such that the radiation pattern is not easily controllable. An antenna of this type is described in IEEE Transactions on Broadcasting, Vol. BC-22, No. 3, September 1976, pages 91-96, in an article entitled "A New CP Antenna for Television Broadcast Service." Also, prior art antennas generally require a center tapped transformer to transform an unbalanced feed to a balanced feed.
One type of cup antenna is the cup turnstile, which has a pair of dipoles that provide circularly polarized radiation that is distributed substantially uniformly in all directions. U.S. Pat. No. 3,740,754 describes a cup turnstile antenna having a pair of dipoles formed from four tubular rods serving as monopoles. The patent describes an antenna in which a feed line is passed through an impedance transformer to provide a separate coaxial line for each monopole. The patent is directed to an implementation of an antenna having a pair of dipoles and a pair of feed lines which are coupled to a pair of transformers. Separate coaxial lines are connected to each of the four monopoles and to two transformers for exciting the monopole elements. The transformers are needed to transform an unbalanced input signal to a balanced output signal. Also the transformer serves to provide the reactance needed to realize broadband operation.